Walgreen Coast

This post includes parts of the Eights Coast, Walgreen Coast, and Bakutis Coast. The Eights Coast extends between Pfrogner Point (S72o37’ W89o35’) and Cape Waite (S72o42’ W103o1’) The Walgreen Coast extends from Cape Waite to Cape Herlacher (S73o52’ W114o12’), and the Bakutis Coast extends west of Cape Herlacher to Dean Island (S74o42’ W127o5’). These points are on the Amundsen Sea embayment, an area fed by two large glaciers and smaller ones (Haynes, Pope, Smith, and Kohler), all of which are retreating (Blaustein, 2014). The West Antarctic Coast is generally bordered by ice shelves, which up until now have buttressed ice streams from the continental glaciers and slowed their discharge. These ice shelves are also losing mass, reducing the buttressing effect (Paolo, Fricker, and Padman, 2015)

Glaciers flowing into the Amundsen Sea along the Walgreen Coast, especially the large Pine Island (S75o10’ W100o0’) and Thwaites (S75o30’ W106o45’) glaciers, exhibit the largest ice mass loss of any glaciers on Earth. Ice loss occurs as above-freezing water flows underneath the glaciers and melts them at their grounding line—the point where the glacier loses contact with bedrock and goes afloat to become an ice shelf. Problems with melting of these glaciers pre-dates recent global warming. In the 1940s, warm ocean waters from an El Nino event began an incursion beneath Pine Island Glacier. This warm water remained under the glacier and never refroze when the sea waters became colder in subsequent decades (Smith et al., 2017; Voosen, 2016). In more recent years, above-freezing water re-entered the areas underneath these glaciers, attacking the grounding lines, which are below sea level by several hundred meters. The retreat of grounding lines raises fears of catastrophic collapse and rapid sea level rise (Silvano et al., 2018).

Thwaites Glacier is now thinning as much as 4 meters per year and its grounding line is migrating inland (Milillo et al., 2019). This melting is likely to continue this century, with grounding lines retreating about 1 km per year. However, as the glaciers become smaller, it is expected that underlying rock being weighted down by the glacial ice will rebound and change the grounding line in the 23rd century (Larour et al., 2019; Steig, 2019).  This bedrock uplift in response to ice loss delays the collapse of the West Antarctic ice sheet under moderate warming scenarios (Barletta et al., 2018).

Ellsworth Land Tundra ecoregion is east of Pine Island Glacier and includes the Jones Mountains, Thurston Island, and Hudson Nunatuks, which are volcanic cones extending above the ice sheet. On Thurston Island are nunatuks which extend above the ice and are called the Walker Mountains. On the Noville Peninsula of Thurston Island is the Sikorski Glacier (S71o50’ W98o30’), an Important Bird Area for the emperor penguin. Four island groups in the Amundsen Sea are also Important Bird Areas. Brownson Islands (S74o10’ W103o30’) are an important bird area for the emperor penguin and seabirds. Edwards Islands (S73o50’ W103o10’), Schaefer Islands (S73o39’ W103o20’), and Lindsey Islands (S73o38’ W103o10’) are important bird areas for the adélie penguin and seabirds (Harris et al., 2015).

Marie Byrd Land Tundra includes the Walgreen Coast and Bakutis Coast west of Pine Island Glacier. On the Bear Peninsula at Hummer Point (S74o20’ W110o20’) is an Important Bird Area for the emperor penguin (Harris et al., 2015). Scattered throughout Marie Byrd Land inland of the glaciers and ice shelves are large volcanoes, such as Mount Frakes (S76o48’ W117o42’) and Mount Takahe (S76o17’ W112o5’) in the Crary Mountains and Toney Mountain (S75o48’ W115o50’ in the Kohler Range. All three volcanoes reach 11,000 to 12,000 feet in elevation. Further to the south is the 4,000 to 6,000-foot Hollick-Kenyon Plateau.

References

Barletta, Valentina R., et al., 2018. Observed rapid bedrock uplift in Amundsen Sea embayment promotes ice-sheet stability. Science 360:1335-1339. 10.1126/science.aao1447.

Blaustein, Richard J. 2014. Antarctic Tipping Points—the fate of the Amundsen Sea glaciers. www.nature.com/scitable/blog/eyes-on-environment/antarctic_tipping_points_the_fate.

Harris, C.M., et al. 2015. Important Bird Areas in Antarctica 2015. BirdLife International and Environmental Research and Assessment Ltd., Cambridge, England.

Larour, E., et al. 2019. Slowdown in Antarctic mass loss from solid Earth and sea-level feedbacks. Science 364:969. 10.1126/science.aav7908.

Milillo, P., et al. 2019. Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica. Science Advances 5:eaau3433. 10.1126/sciadv.aau3433.

Paolo, Fernando S., Helen A. Fricker, and Laurie Padman. 2015. Science 348:327-331. 10.1126/science.aaa0940.

Silvano, Alessandro et al., 2018. Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic bottom water. Science Advances 4:eaap9467. 10.1126/sciadv.aap9467.

Smith, J.A. et al. 2017. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier. Nature 541:177-180. 10.1038/nature20136.

Steig, Eric J. 2019. How Fast will the Antarctic Ice Sheet Retreat? Science 364:936-937. 10.1126/science.aax2626.

Voosen, Paul. 2016. In the 1940s, warm oceanwaters found Achilles’s heel of crucial Antarctic ice sheet. 10.1126/science.aal0421. https://www.sciencemag.org/news/2016/11/1940s-warm-ocean-waters-found-achilless-heel-crucial-antarctic-ice-sheet.

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